Thermostable DNA polymerase from carboxydothermus hydrogenoformans

ABSTRACT

A DNA polymerase from a thermophilic eubacterium is provided. The DNA polymerase shows magnesium ion dependent reverse transcriptase activity and 3&#39;-5&#39; exonuclease activity. The invention also includes recombinant plasmids and transformed host cells capable of producing the enzyme. The enzyme is classified into class EC 2.7.7.7., a DNA nucleotidyl transferase DNA-directed type.

The present invention relates to a thermostable enzyme which is a DNA polymerase obtainable from Carboxydothermus hydrogenoformans. Furthermore, the present invention relates to the field of molecular biology and provides improved methods for the replication and amplification of deoxyribonucleic (DNA) and ribonucleic acid (RNA) sequences. In a preferred embodiment, the invention provides a method for synthesizing a complementary DNA copy from an RNA template with a thermoreactive DNA polymerase. In another aspect, the invention provides methods for amplifying a DNA segment from an RNA or DNA template using a thermostable DNA polymerase (RT-PCR or PCR).

Heat stable DNA polymerases (EC 2.7.7.7. DNA nucleotidyltransferase. DNA-directed) have been isolated from numerous thermophilic organisms (for example: Kaledin et al. (1980). Biokimiva 45, 644-651; Kaledin et al. (1981) Biokimiva46, 1247-1254; Kaledin et al. (1982) Biokimiya 47, 1515-1521; Ruttimann et al. (1985) Eur. J. Biochem. 149, 41-46; Neuner et al. (1990) Arch. Microbiol. 153, 205-207). For some organisms, the polymerase gene has been cloned and expressed (Lawyer et al. (1989) J. Biol. Chem. 264, 6427-6437; Engelke et al. (1990) Anal. Biochem. 191, 396-400; Lundberg et al. (1991) Gene 108, 1-6; Perler et al. (1992) Proc. Natl. Acad. Sci. USA 89, 5577).

Thermophilic DNA polymerases are increasingly becoming important tools for use in molecular biology and there is growing interest in finding new polymerases which have more suitable properties and activities for use in diagnostic detection of RNA and DNA, gene cloning and DNA sequencing. At present, the thermophilic DNA polymerases mostly used for these purposes are from Thermus species like Taq polymerase from T. aquaticus (Brock et al. (1969) J. Bacteriol. 98. 289-297)

Reverse transcription is commonly performed with viral reverse transcriptases like the enzymes isolated from Avian myeloblastosis virus or Moloney murine leukemia virus, which are active in the presence of Magnesium ions but have the disadvantages to possess RNase H-activity, which destroys the template RNA during the reverse transcription reaction and have a temperature optimum at at 42° C. or 37° C., respectively.

Alternative methodes are described using the reverse transcriptase activity of DNA polymerases of thermophilic organisms which are active at higher temperatures. Reverse transcription at higher temperatures is of advantage to overcome secondary structures of the RNA template which could result in premature termination of products. Thermostable DNA polymerases with reverse transcriptase activities are commonly isolated from Thermus species. These DNA polymerases however, show reverse transcriptase activity only in the presence of Manganese ions. These reaction conditions are suboptimal, because in the presence of Manganese ions the polymerase copies the template RNA with low fidelity.

Another feature of the commonly used reverse transcriptases is that they do not contain 3′-5′ exonuclease activity. Therefore, misincorporated nucleotides cannot be removed and thus the cDNA copies from the template RNA may contain a significant degree of mutations.

Therefore, it is desirable to develop a reverse transcriptase

which acts at higher temperatures to overcome secondary structures in the template to avoid premature termination of the reaction and to assure the production of cDNA without deletions

which is active in the presence of Magnesium ions in order to prepare cDNA from RNA templates with higher fidelity and

which has 3′-5′-exonuclease in order to remove misincorporated nucleotides before continuation of DNA synthesis and to produce a product with a low mutation frequency.

The present invention adresses these needs and provides a heat stable DNA polymerase active at higher temperatures which has reverse transcriptase activity in the presence of magnesium ions and and which has 3′-5′ exonuclease activity.

It is an object of this invention to provide a polymerase enzyme (EC 2.7.7.7.), characterised in that it has reverse transcriptase activity in the presence of magnesium ions as well as in the presence of manganese ions. In another aspect the invention comprises a DNA polymerase isolated from Carboxydothermus hydrogenoformans (Deutsche Sammiung von Mikroorganismen und Zellkulturen GmbH, Mascheroder Weg 1b, D-38124 Braunschweig, DSM No. 8979). In a further aspect the invention comprises a DNA polymerase having reverse transcriptase activity in the presence of magnesiums ions and in the substantial absence of manganese ions. In a further aspect the invention comprises a DNA polymerase having a molecular mass of about 100 to 105 kDa as determined by in situ PAGE analysis. In a further aspect the invention comprises a reverse transcriptase which is thermostable. In a further aspect the invention comprises a DNA polymerase having 3′-5′-exonuclease activity. In a further aspect the invention comprises a recombinant DNA sequence that encodes DNA polymerase activity of the microorganism Carboxidothermus hydrogenoformans. In a related aspect the DNA sequence is depicted as SEQ ID No. 7. In a second related aspect the invention comprises a recombinant DNA sequence that encodes essentially amino acid residues 1 to 831. In a further aspect the invention comprises a recombinant DNA plasmid that comprises the DNA sequence of the invention inserted into plasmid vectors and which can be used to drive the expression of the thermostable DNA polymerase of Carboxydothermus hydrogenoformans in a host cell transformed with the plasmid. In a further aspect the invention includes a recombinant strain comprising the vector pDS56 carrying the Carboxydothermus hydrogenoformans DNA polymerase gene and designated pAR 4. The E.coli strain (BL21 DE3)pUBS520) carrying the plasmid pAR4 was deposited on the Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH, Mascheroder Weg 1b, D-38124 Braunschweig DSM No. 11179) and is designated AR96.

In referring to a peptide chain as being comprised of a series of amino acids “substantially or effectively” in accordance with a list offering no alternatives within itself, we include within that reference any versions of the peptide chain bearing substitutions made to one or more amino acids in such a way that the overall structure and the overall function of the protein composed of that peptide chain is substantially the same as—or undetectably different to—that of the unsubstituted version. For example it is generally possible to exchange alanine and valine without greatly changing the properties of the protein, especially if the changed site or sites are at positions not critical to the morphology of the folded protein.

The DNA polymerase is “thermostable” meaning that it is stable to heat and preferentially active at higher temperatures, especially the high temperatures used for denaturation of DNA strands. More particularly, the thermostable DNA polymerases are not substantially inactivated at the high temperatures used in polymerase chain reactions.

The term “reverse transcriptase” describes a class of polymerases characterized as RNA-dependent DNA polymerases. All known reverse transcriptases require a primer to synthesize a DNA transcript from an RNA template. Historically, reverse transcriptase has been used primarily to transcribe mRNA into cDNA which can then be cloned into a vector for further manipulation.

Other definitions are used in a manner consistent with the art.

Carboxydothermus hydrogenoformans was isolated from a hot spring in Kamchatka by V. Svetlichny. A sample of C. hydrogenoformans was deposited on the Deutsche Sammlung von Mikroorganismen und Zelikulturen GmbH (DSM) under the terms of the BudaPest Treaty and received Accession Number DSM 8979. The thermostable polymerase isolated from Carboxydothermus hydrogenoformans has a molecular weight of 100 to 105 KDa and retains more than 60% of its initial activity after heating to 95° C. for 30 minutes. The thermostable enzyme possesses a 5′-3′ polymerase activity, a 3′-5′-exonuclease activity, a 5′-3′-exonuclease activity and a reverse transcriptase-activity which is Mg⁺⁺-dependent. The polymerase according to the present invention has reverse transcriptase activity in the presence of magnesium ions and in the substantial absence of manganese ions. The thermostable enzyme may be native or recombinant and may be used for first- and second-strand cDNA synthesis, in cDNA cloning, DNA sequencing, DNA labeling and DNA amplification.

For recovering the native protein C.hydrogenoformans may be grown using any suitable technique, such as the technique described by Svetlichny et al. (1991) System. Appl. Microbiol., 14, 205-208. After cell growth one preferred method for isolation and purification of the enzyme is accomplished using the multi-step process as follows:

The cells are thawed, suspended in buffer A (40 mM Tris-HCl, pH 7.5, 0.1 mM EDTA, 7 mM 2-mercaptoethanol. 0.4 M NaCl, 10 mM Pefabloc) and lysed by twofold passage through a Gaulin homogenizer. The raw extract is cleared by centrifugation, the supernatant dialyzed against buffer B (40 mM Tris-HCl, pH 7.5, 0.1 mM EDTA, 7 mM 2-mercaptoethanol, 10% Glycerol) and brought onto a column filled with Heparin-Sepharose (Pharmacia). In each case the columns are equilibrated with the starting solvent and after the application of the sample washed with the threefold of its volume with this solvent. Elution of the first column is performed with a linear gradient of 0 to 0.5 M NaCl in Buffer B. The fractions showing polymerase activity are pooled and ammonium sulfate is added to a final concentration of 20%. This solution is applied to a hydrophobic column containing Butyl-TSK-Toyopearl (TosoHaas). This time the column is eluted with a falling gradient of 20 to 0% ammonium sulfate. The pool containing the activity is dialysed and again transferred to a column, this time with DEAE-Sepharose (Pharmacia), and eluted with a linear gradient of 0-0.5 M NaCl in buffer B. The fourth column contains Tris-Acryl-Blue. (Biosepra) and is eluted as in the preceding case.

Finally the active fractions are dialyzed against buffer C (20 mM Tris-HCl, pH 7.5, 0.1 mM EDTA, 7.0 mM 2-mercaptoethanol. 100 mM NaCl, 50% Glycerol.

Isolation of recombinant DNA polymerase from Carboxydothermus hydrogenoformans may be performed with the same protocol or with other commonly used procedures.

DNA polymerase activity was measured by incorporation of digoxigenin-labeled dUTP into the sythesized DNA and detection and quantification of the incorporated digoxigenin essentially according to the method described in Hölke, H.-J.; Sagner, G; Kessler, C. and Schmitz. G. (1992) Biotechniques 12, 104-113.

Determination of reverse transcriptase activity is performed essentially as described for determination of DNA polymerase activity except that the reaction mixture consists of the components as described by example 3. In situ PAGE analysis of polymerase activity and reverse transcriptase activity was performed essentially according to the method described by Spanos A. and Hübscher U. ((1983) Methods in Enzymology 91, 263-277). Some minor, but essential modifications to the original method are, that the renaturation of the SDS-denatured polypeptides is performed in the presence of magnesium ions (3 mM) and dATP (0.5-1 μM) to assist refolding.

3′-5′ exonuclease activity is commonly referred as “proofreading” or “editing” activity of DNA polymerases. It is located in the small domain of the large fragment of Type A polymerases. This activity removes mispaired nucleotides from the 3′ end of the primer terminus of DNA in the absence of nucleoside triphosphates (Kornberg A. and Baker T. A.(1992) DNA Replication W. H. Freemann & Company, New York). This nuclease action is suppressed by deoxynucleoside triphosphates if they match to the template and can be incorporated into the polymer.

The 3′- 5′ exonuclease activity of the claimed DNA polymerase can be measured as degradation or shortening of a 5′-digoxygenin-labeled oligonucleotide annealed to template DNA in the absence or presence of deoxyribonucleoside triphosphates or on DNA fragments in the absence or presence of deoxyribonucleoside triphosphates.

Carboxydothermus hydrogenoformans DNA polymerase is the first DNA polymerase isolated from thermophilic eubacteria with a higher activity in the presence of magnesium ions than in the presence of manganese ions as shown in FIG. 1. Compaired to the DNA polymerase activity the reverse transcriptase activity in the presence of magnesium is relatively high. This is shown—in comparison with DNA polymerases from T.filiformis, A.thermophilum and the most commonly used DNA polymerase for reverse transcription T.thermophilus in FIG. 6. The reverse transcriptase activity in dependence of magnesium is of advantage since the DNA polymerases synthesize DNA with higher fidelity in the presence of magnesium than in the presence of manganese (Beckmann R. A. et al. (1985) Biochemistry 24, 5810-5817; Ricchetti M. and Buc H. (1993) EMBO J. 12, 387-396). Low fidelity DNA synthesis is likely to lead to mutated copies of the original template. In addition, Mn²⁺ ions have been implicated in an increased rate of RNA degradation, particularly at higher temperatures and this can cause the synthesis of shortened products in the reverse transcription reaction.

The DNA sequence (SEQ ID No.: 7) of Carboxydothermus hydrogenoformans polymerase and the derived amino acid sequence of the enzyme are shown in FIG. 5. The molecular weight deduced from the sequence is 94 348 Da, in SDS polyacrylamide gel electrophoresis however the Carboxydothermus hydrogenoformans polymerase has an electrophoretic mobility higher than E.coli pol I (109 kDa) and a lower mobility than Taq polymerase (94 kDa) and Klenow fragment (76 kDa) as shown in FIG. 2. Comparing the migration properties of Taq and E.coli DNA polymerases with those of Carboxydothermus hydrogenoformans polymerase a molecular weight of 100 to 105 kDa can be deduced. Since the Carboxydothermus hydrogenoformans polymerase isolated from the native strain has the same migration properties as the recombinant enzyme the “slower” migration during SDS gel electrophoresis must rather be a property of the enzyme than a cloning artefact. A possible explanation for this phenomenon could be that this enzyme which is derived from a thermophilic organism has a very stable structure which is not completely unfolded under the standard denaturation conditions used.

The production of a recombinant form of Carboxydothermus hydrogenoformans DNA polymerase generally includes the following steps: chromosomal DNA from Carboxydothermus hydrogenoformans is isolated by treating the cells with detergent e.g. SDS and a proteinase e.g. Proteinase K. The solution is extracted with phenol and chloroform and the DNA purified by precipitation with ethanol. The DNA is dissolved in Tris/EDTA buffer and the gene encoding the DNA polymerase is specifically amplified by the PCR technique using two mixed oligonucleotides (primer 1 and 2). These oligo-nucleotides. described by SEQ ID No.: 1 and SEQ ID No.: 2. were designed on the basis of conserved regions of family A DNA polymerases as published by Braithwaite D. K. and Ito J., 1993, Nucl. Acids Res. Vol. 21, p. 787-802. The specifically amplified fragment is ligated into an vector, preferably the pCR™ II vector (Invitrogen) and the sequence is determined by cycle-sequencing. Complete isolation of the coding region and the flanking sequences of the DNA polymerase gene can be performed by restriction fragmentation of the Carboxydothermus hydrogenoformans DNA with another restriction enzyme as in the first round of screening and by inverse PCR (Innis et al., (1990) PCR Protocols; Academic Press, Inc., p. 219-227). This can be accomplished with synthesized oligonucleotide primers binding at the outer DNA sequences of the gene part but in opposite orientation. These oligonucleotides described by SEQ ID Nos. 3 and 4, were designed on the basis of the sequences which were determined by sequencing of the first PCR product described above. As template Carboxydothermus hydrogenoformans DNA is used which is cleaved by restriction digestion and circularized by contacting with T4 DNA ligase. To isolate the coding region of the whole polymerase gene, another PCR is performed using primers as shown in SEQ ID Nos. 5 and 6 to amplify the complete DNA polymerase gene directly from genomic DNA and introducing ends compatible with the linearized expression vector.

SEQ ID No. 1:

Primer 1: 5′-CCN AAY YTN CAR AAY ATH-3′

SEQ ID No. 2:

Primer 2: 5′-YTC RTC RTG NAC YTG-3′

SEQ ID No. 3:

Primer 3: 5′-GGG CGA AGA CGC TAT ATT CCT GAG C-3′

SEQ ID NO. 4:

Primer 4: 5′-GAA GCC TTA ATT CAA TCT GGG AAT AAT C-3′

SEQ ID NO. 5:

Primer 5: 5′-CGA ATT CAA TCC ATG GGA AAA GTA GTC CTG GTG GAT-3′

SEQ ID NO. 6:

Primer 6: 5′-CGA ATT CAA GGA TCC TTA CTT CGC TTC ATA CCA GTT-3′

The gene is operably linked to appropriate control sequences for expression in either prokaryotic or eucaryotic host/vector systems. The vector preferably encodes all functions required for transformation and maintenance in a suitable host, and may encode selectable markers and/or control sequences for polymerase expression. Active recombinant thermostable polymerase can be produced by transformed host cultures either continuously or after, induction of expression. Active thermostable polymerase can be recovered either from host cells or from the culture media if the protein is secreted through the cell membrane.

It is also preferable that Carboxydothermus hydrogenoformans thermostable polymerase expression is tightly controlled in E.coli during cloning and expression. Vectors useful in practicing the present invention should provide varying degrees of controlled expression of Carboxydothermus hydrogenoformans polymerase by providing some or all of the following control features: (1) promoters or sites of initiation of transcription, either directly adjacent to the start of the polymerase gene or as fusion proteins, (2) operators which could be used to turn gene expression on or off, (3) ribosome binding sites for improved translation, and (4) transcription or translation termination sites for improved stability. Appropriate vectors used in cloning and expression of Carboxydothermus hydrogenoformans polymerase include, for example, phage and plasmids. Example of phage include lambda gtII (Promega), lambda Dash (Stratagene) lambda ZapII (Strata-gene). Examples of plasmids include pBR322, pBTac2 (Boehringer Mannheim), pBluescript (Stratagene), pSP73 (Promega), pET3A (Rosenberg, supra, (1987) Gene 56:125-135), pASK75 (Biometra), pDS56 (Stüber, D., Matile, H. and Garotta G. (1990) Immunological Methods, Letkovcs, I. and Pernis, B., eds.) and pET11C (Studier, F. W. (1990) Methods in Enzymology, 185:60-89). According to the present invention the use of a plasmid has shown to be advantageously, particularly pDS56. The Plasmid pDS56 carrying the Carboxydothermus hydrogenoformans DNA polymerase gene is then designated pAR4.

Standard protocols exist for transformation, phage infection and cell culture (Maniatis, et al. (1982) Molecular Cloning: A Laboratory Manual, Cold Spring Harbour Laboratory Press). Of the numerous E.coli strains which can be used for plasmid transformation, the preferred strains include JM110 (ATCC 47013), LE392 pUBS 520 (Maniatis et al. supra; Brinkmann et al., (1989) Gene 85:109-114;), JM101 (ATCC No. 33876), XL1 (Stratagene), and RR1 (ATCC no. 31343), BL21 (DE3) pUBS520 (Brinkmann, U. et al. (1989) Gene 85, 109-114) and BL21 (DE3) plysS (Studier, F. W. et al., (1990) Methods in Enzymology, supra). According to the present invention the use of the E. coli strain BL21 (DE3) pUBS520 has shown to be advantageously. The E. coli strain BL21 (DE3) pUBS520 transformed with the plasmid pAR4 is then designated AR96(DSM No. 11179). E.coli strains XL1-Blue (Stratagene), and ER1458 (Raleigh, E. A. et al., (1988) Nucleic Acids Research 16:1563-1575) are among the strains that can be used for lambda phage, and Y1089 can be used for lambda gt11 lysogeny. The transformed cells are preferably grown at 37° C. and expression of the cloned gene is induced with IPTG.

Isolation of the recombinant DNA polymerase can be performed by standard techniques. Separation and purification of the DNA polymerase from the E.coli extract can be performed by standard methods. These methods include, for example, methods utilizing solubility such as salt precipitation and solvent precipitation, methods utilizing the difference in molecular weight such as dialysis, ultra-filtration, gel-filtration, and SDS-polyacrylamide gel electrophoresis, methods utilizing a difference in electric charge such as ion-exchange column chromatography, methods utilizing specific interaction such as affinity chromatography, methods utilizing a difference in hydrophobicity such as reversed-phase high performance liquid chromatography and methods utilizing a difference in isoelectric point such as isoelectric focussing electrophoresis.

The present invention provides improved methods for efficiently transcribing RNA and amplifying RNA or DNA. These improvements are achieved by the discovery and application of previously unknown properties of thermoactive DNA polymerases.

The thermostable enzyme of this invention may be used for any purpose in which such enzyme activity is necessary or desired. In a particularly preferred embodiment, the enzyme catalyzes the nucleic acid amplification reaction known as PCR. This process for amplifying nucleic acid sequences is disclosed and claimed in U.S. Pat. No. 4,683,202. The PCR nucleic acid amplification method involves amplifying at least one specific nucleic acid sequence contained in a nucleic acid or a mixture of nucleic acids and produces double-stranded DNA. Any nucleic acid sequence, in purified or nonpurifled form, can be utilized as the starting nucleic acid(s), provided it contains or is suspected to contain the specific nucleic acid sequence desired. The nucleic acid to be amplified can be obtained from any source, for example, from plasmids such as pBR322, from cloned DNA or RNA, from natural DNA or RNA from any source, including bacteria, yeast, viruses, organelles, and higher organisms such as plants and animals, or from preparations of nucleic acids made in vitro.

DNA or RNA may be extracted from blood, tissue material such as chorionic villi, or amniotic cells by a variety of techniques. See, e.g., Maniatis et al., 1982, Molecular Cloning: A Laboratory Manual (Cold Spring Harbor Laboratory, Cold Spring Harbor, N.Y.) pp. 280-281. Thus the process may employ, for example, DNA or RNA, including messenger RNA, which DNA or RNA may be single-stranded or double-stranded. In addition, a DNA-RNA hybrid which contains one strand of each may be utilized.

The amplification of target sequences in DNA or from RNA may be performed to proof the presence of a particular sequence in the sample of nucleic acid to be analyzed or to clone a specific gene. DNA polymerase from Carboxydothermus hydrogenoformans is very useful for these processes. Due to its 3′-5 ′ exonuclease activity it is able to synthesize products with higher accuracy as the reverse transcriptases of the state of the art.

DNA polymerase from Carboxydothermus hydrogenoformans may also be used to simplify and improve methods for detection of RNA target molecules in a sample. In these methods DNA polymerase from Carboxydothermus hydrogenoformans may catalyze: (a) reverse transcription, (b) second strand cDNA synthesis, and. if desired, (c) amplification by PCR The use of DNA polymerase from Carboxydothermus hydrogenoformans in the described methods would eliminate the previous requirement of two sets of incubation conditions which are necessary due to the use of different enzymes for each step. The use of DNA polymerase from Carboxydothermus hydrogenoformans may be used to perform RNA reverse transcription and amplification of the resulting complementary DNA with enhanced specificity and with fewer steps than previous RNA cloning and diagnostic methods.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the relative reverse transcriptase activity of DNA polymerase from Carboxydothermus hydrogenoformans in dependence of magnesium and manganese salt.

FIG. 2 shows a photograph of a DNA polymerase assay performed in situ. The activity of DNA polymerase from Carboxydothermus hydrogenoformans and reference polymerases is detected in situ. A fraction of DNA polymerase from C. hydrogenoformans and reference enzyme were submitted to electrophoresis on a SDS-polyacrylamide gel containing activated calf thymus DNA. After electrophoresis the SDS was removed, the proteins were renatured and incubated at 65° C. in the presence of magnesium salt, dNTPs and digoxigenin labeled dUTP to allow DNA synthesis. The nucleic acid was blotted to a nylon membrane and the newly synthesized DNA detected by a chemiluminescence reaction.

FIG. 3 shows the thermostability of DNA polymerase from Carboxydothermus hydrogenoformans. Aliquots of the DNA polymerase were incubated for 30 min. at the temperatures indicated in the figure, and subsequently the remaining enzyme activity was determined.

FIG. 4 shows the analysis for 3 ′-5 ′-exonuclease activity of DNA polymerase from Carboxydothermus hydrogenoformans in comparison with DNA polymerase from Thermus aquaticus and Pyrococcus woeseii. The analysis is performed in the presence or absence of dNTPs. A 22mer primer labeled with digoxigenin at the 5 ′-end was annealed to a 34mer template DNA leaving a 12 bp 5′ overhang of template DNA. DNA polymerases from Carboxydothermus hydrogenoformans, Thermus aquaticus and Pyrococcus woeseii were incubated with this substrate in the presence of magnesium with or without dNTPs. The products were separated on a sequencing gel, blotted to a nylon membrane and detected by a chemiluminescence reaction.

FIG. 5 shows the DNA sequence of the polymerase gene of Carboxydothermus hydrogenoformans with SEQ ID No.: 7 and the derived peptide sequence of the DNA polymerase protein with SEQ ID No. 8.

FIG. 6 shows a comparison of the reverse transcriptase activity thermostable DNA polymerases Carboxydothermus hydrogenoformans, Anaerocellum thermophilum, Thermus filiformis (Pacific Enzymes) and Thermus thermophilus. Similar amounts (units) of the DNA polymerases were analyzed. Each enzyme was tested for DNA polymerase activity, for reverse tanscriptase activity in the presence of Mg⁺⁺ (5 mM) and reverse transcriptase activity in the presence of Mn⁺⁺ (1 mM) under the reaction conditions optimal for the individual enzymes. DNA synthesis was measured by incorporation of digoxigenin-labeled nucleotides. In order to compare the ratio of DNA polymerase to reverse transcriptase activity, the relative light units (RLU) measured in the DNA polymerase assay was set to 100. The RLUs measured in the reverse transcriptase activity tests are expressed as percent of the polymerase activity.

EXAMPLE 1 Detection of Endonuclease, Exonuclease and Ribonuclease Activities

Absence of endonuclease activity: 1 μg of plasmid DNA is incubated for 4 hours with an excess of purified DNA polymerase in 50 μl of test buffer with a paraffin oil overlay at 72° C.

Absence of nonspecific exonuclease activity: 1 μg of EcoRI/HindIII-fragments of lambda DNA are incubated in 100 μl of test buffer in the absence and presence of dNTPs (1 mM final concentration each) with an excess of purified DNA polymerase for 4 hours at 72° C.

Absence of ribonuclease activity: 3 μg of MS2 RNA are incubated with an excess of DNA polymerase in 20 μl of test buffer for 4 hours at 72° C. The RNA is subsequently analyzed by electrophoresis in a MOPS gel (Maniatis et al. (1982) Molecular Cloning: A Laboratory Manual, Cold Spring Harbor, N.Y.).

EXAMPLE 2 Determination of DNA Polymerase Activity

DNA polymerase activity was measured by incorporation of digoxigenin-labeled dUTP into the sythesized DNA and detection and quantification of the incorporated digoxigenin essentially according to the method described in Höltke, H.-J.; Sagner. G. Kessler, C. and Schmitz, G. (1992) Biotechniques 12, 104-113. The reaction is performed in a reaction volume of 50 μl containing 1 or 2 μl of diluted (0.05 U-0.01 U) DNA polymerase and 50 mM Tris-HCl, pH 8.5; 12.5 mM (NH₄)₂SO₄; 10 mM KCl; 5 mM MgCl₂; 10 mM 2-mercaptoethanol; 33 μM dNTPs; 200 μg/ml BSA;12 μg of DNAse 1-activated DNA from calf thymus and 0.036 μM digoxigenin-dUTP.

The samples are incubated for 30 min. at 72° C., the reaction is stopped by addition of 2 μl 0.5 M EDTA. and the tubes placed on ice. After addition of 8 μl 5 M NaCl and 150 μl of Ethanol (precooled to −20° C.) the DNA is precipitated by incubation for 15 min. on ice and pelleted by centrifugation for 10 min at 13000×rpm and 4° C. The pellet is washed with 100 μl of 70% Ethanol (precooled to −20° C.) and 0.2 M NaCl, centrifuged again and dried under vacuum.

The pellets are dissolved in 50 μl Tris-EDTA (10 mM/0.1 mM; pH 7.5). 5 μl of the sample are spotted into a well of a nylon membrane bottomed white microwell plate (Pall Filtrationstechnik GmbH, Dreieich, FRG, product no: SM045BWP). The DNA is fixed to the membrane by baking for 10 min. at 70° C. The DNA loaded wells are filled with 100 l of 0.45 μm-filtrated 1% blocking solution (100 mM maleic acid, 150 mM NaCl, 1% (w/v) casein, pH 7.5). All following incubation steps are done at room temperature. After incubation for 2 min. the solution is sucked through the membrane with a suitable vacuum manifold at −0.4 bar. After repeating the washing step, the wells are filled with 100 μl of a 1:10 000-dilution of Anti-digoxigenin-AP, Fab fragments (Boehringer Mannheim, FRG, no: 1093274) diluted in the above blocking solution. After incubation for 2 min. and sucking this step is repeated once. The wells are washed twice under vacuum with 200 μl each time washing-buffer 1 (100 mM maleic-acid, 150 mM NaCl, 0.3%(v/v) Tween™ 20 (Poly(oxyethylen)_(n)-Sorbitan-monolaurat), pH 7.5). After washing another two times under vacuum with 200 μl each time washing-buffer 2 (10 mM Tris-HCl. 100 mM NaCl, 50 mM MgCl₂, pH 9.5) the wells are incubated for 5 min. with 50 μl of CSPD™ (Boehringer Mannheim. no: 1655884), diluted 1:100 in washing-buffer 2, which serves as a chemiluminescent substrate for the alkaline phosphatase. The solution is sucked through the membrane and after 10 min. incubation the RLU/s (Relative Light Unit per second) are detected in a Luminometer e.g. MicroLumat LB 96 P (EG&G Berthold, Wilbad, FRG).

With a serial dilution of Taq DNA polymerase a reference curve is prepared from which the linear range serves as a standard for the activity determination of the DNA polymerase to be analyzed.

EXAMPLE 3 Determination of Reverse Transcriptase Activity

The assay is performed essentially as described for determination of DNA polymerase activity except that the reaction mixture consists of the following components: 1 μg of polydA-(dT)₁₅, 33 μM of dTTP, 0.36 μM of digoxigenin-dUTP, 200 mg/ml BSA, 10 mM Tris-HCl, pH 8.5, 20 mM KCl, 5 mM MgCl₂, 10 mM DTE and various amounts of DNA polymerase The incubation temperature used is 50° C.

EXAMPLE 4 Detection of DNA Polymerase Activity in Situ

In situ PAGE analysis of polymerase activity and reverse transcriptase activity was performed essentially according to the method described by Spanos A. and Hübscher U. (1983) Methods in Enzymology 91, 263-277. Some minor, but essential modifications to the original method are, that the renaturation of the SDS-denatured polypeptides is performed in the presence of magnesium ions (3 mM) and DATP (0.5-1 μM) to assist refolding.

In Brief the Method is as Follows

After separation of the polypeptides from either crude cell extracts or purified samples on denaturing 8% polyacrylamide gels (stacking gel 5% acrylamide) which contain 150 μg activated calf thymus DNA per ml gel volume, the gels are washed four times for 30 min each at room temperature with moderate shaking in excess renaturation buffer (Tris-HCl, 50 mM, pH 8.3; EDTA, 1 mM; 2-mercaptoethanol, 3 mM; KCl, 50 mM; glycerol, 5-10%) to remove SDS. Then the gels are incubated overnight in the same buffer, including 3 mM MgCl₂ and 0.5-1 μM dATP at 4° C. without agitation. The first four washes are repeated the next day with renaturation buffer. Subsequent to the removal of SDS and renaturation of the proteins the gel is transferred into reaction mixture, consisting of Tris-HCl, 50 mM, pH 8.3; KCl, 50 mM; DTT, 3 mM; MgCl₂, 7 mM, 12 μM of each dATP, dCTP, dGTP, 8 μM dTTP and 4 μM Dig-dUTP; 10% (vol/vol) glycerol. Gels were first incubated under shaking at room temperature for one hour and then warmed up stepwise to 37° C., 45° C., 55° C., 65° C. and 72° C. At each incubation temperature DNA synthesis was allowed to proceed for 60 minutes.

After DNA synthesis, the DNA is transferred either by contact blotting or by capillary blotting (15×SSC, Maniatis et al., supra) to nylon membranes (Boehringer Mannheim, GmbH) and crosslinked.

The detection of newly synthesized, digoxigenin-labeled DNA followed the procedure given in the previous section (Determination of DNA polymerase activity).

For molecular weight determination marker polymerases of known molecular weight (e.g. Klenow-polymerase, Pol I, Taq polymerase, Tth polymerase, HIV RT, M-MuLV RT) are applied onto the same gel, but different lanes.

The molecular weight of the claimed DNA polymerase according to this method is 100 to 105 kDa.

EXAMPLE 5 Detection of 3′-5′ Exonuclease Activity

3′-5 exonuclease activity is commonly referred as “proofreading” or “editing” activity of DNA polymerases. It is located in the small domain of the large fragment of Type A polymerases. This activity removes nucleotides from the 3′ end of the primer terminus of DNA in the absence of nucleoside triphosphates (Komberg A. and Baker T. A.(1992) DNA Replication W. H. Freemann & Company, New York). This nuclease action is suppressed by deoxynucleoside triphosphates if they match to the template and can be incorporated into the polymer.

The 3′-5′ exonuclease activity of the claimed DNA polymerase can be measured as degradation or shortening of a 5′-digoxygenin-labeled oligonucleotide annealed to template DNA in the absence or presence of deoxyribonucleoside triphosphates or on DNA fragments in the absence or presence of deoxyribonucleoside triphosphates.

Degradation of digoxigenin labeled oligonucleotide: The reaction mixture is essentially the same as that for determination of DNA polymerase activity (50 mM Tris-HCl, pH 8.4, 12.5 mM (NH₄)₂SO₄; 10 mM KCl; 5 mM MgCl₂ 10 mM 2-mercaptoethanol), except that the dNTP concentration was reduced to 12.5 μM and activated calf thymus DNA was replaced by 500 fMol primer or template/primer mixture.

The primer sequence is:

SEQ ID NO.8.:

Dig-GCATGGATCCCACTGCCCAGGG (5′ to 3′).

This primer is annealed with template molecules of various 12 bp 5 prime overhangs. DNA polymerase samples of typically 0.1 units are incubated in a total reaction volume of 10 μl for 30 min at 72° C. in a Perkin Elmer thermal cycler. Reactions are stopped by adding an equal volume of formamide-buffer (98% formamide; 10 mM EDTA; bromphenol blue and xylencyanol) and denatured by heating for 10 min at 95° C. Samples are quickly chilled on ice and loaded on a 20% denaturing polyacrylamide/urea sequencing gel. Electrophoresis is performed at 60° C. and 2000 V for 2.5 hours.

After separation DNA is transferred onto a positively charged nylon membrane (Boehringer Mannheim) by contact blotting for 30 min. The DNA is crosslinked to the membrane by UV-irradiation with 120 mJoule (Stratalinker. Stratagene). The membrane is blocked with blocking solution (100 mM maleic-acid, 150 mM NaCl, 1%(w/v) casein. pH is adjusted to 7.5 with 1 M NaOH) at room temperature for at least 30 min. digoxigenin-labeled primer DNA is detected with anti Digoxigenin-AP. Fab-fragments (Boehringer Mannheim, FRG, no 1093274) diluted 1:10000 in blocking solution (30 min at room temperature). Excess unbound antibody is removed by washing 3-4 times (10-15 min, each step) with washing buffer (100 mM maleic-acid, 150 mM NaCl, 0.3% (v/v) Tween™ 20 (Poly(oxyethylen)_(n)-sorbitan-monolaurat), pH 7.5). The membrane is transferred into a buffer containing 10 mM Tris-HCl, 100 mM NaCl, pH 9.5) and washed twice for additional 10-15 min at room temperature. Finally the membrane is soaked with a 1:1000 diluted solution of CDP-Star™ (Boehringer Mannheim). CDP-Star™ serves as a chemiluminiscent substrate for alkaline phosphatase. Then the membrane is transferred on filter paper (Whatman 3MM) to remove excess fluid, positioned between two sheets of transparent overhead foils and exposed to X-ray film. (Chemiluminescent Detection Film, Boehringer Mannheim) for 5-10 min. 3′-5′ exonuclease activity is detected by degradation or shortening of the primer compared with a control (no polymerase added). As negative and positive controls DNA polymerases from Thermus aquaticus (no 3′ to 5′ exonuclease activity) and from Pyrococcus woeseii (exhibiting 3′ to 5′ exonuclease activity) are included.

Degradation of DNA fragments in the presence or absence of deoxynucleoside triphosphates: A series of dilutions of Chy polymerase was incubated for 2 hours at 70° C. with 1 μg of DNA molecular weight marker III (Boehringer Mannheim) in the presence and absence of dNTPs, 1 mM each, in 50 μl of the following incubation buffer: 50 mM Tris-HCl, pH 7.8; 10 mM MgCl₂; 7 mM 2-mercaptoethanol with Paraffin overlay. The DNA fragments were separated on a 1% agarose gel containing ethidium bromide. In the absence of dNTPs a smear of DNA fragments or no DNA could be detected while in the presence of dNTPs the DNA fragments remained undegraded.

EXAMPLE 6 Cloning of the Carboxydothermus hydrogenoformans DNA Polymerase Gene

Preparation of chromosomal DNA from Carboxydothermus hydrogenoformans. 0.8 g biomass of Carboxydothermus hydrogenoformans was suspended in 20 ml 1 M KCl and centrifuged. Then the pellet was resuspended in 4.8 ml SET-buffer (150 mM NaCl, 15 mM EDTA, pH 8.0, 60 mM Tris-HCl, pH 8.0, 50 μg/μl RNaseA), after which 1 ml 20% SDS and 50 μg of proteinase K (10 mg/ml) were added. The mixture was kept at 37° C. for 45 minutes. After extraction with phenol and chloroform the DNA was precipitated with ethanol and dissolved in H₂O. Thus about 4.1 mg of DNA were obtained.

Amplification of Specific DNA by PCR

For amplification of the gene encoding the DNA polymerase of Carboxydothermus hydrogenoformans by the PCR technique two mixed oligonucleotides (primer 1 and 2) were designed on the basis of conserved regions of family A DNA polymerases as published by Braithwaite D. K. and Ito J. (1993) Nucl. Acids Res. 21, 787-802.

SEQ ID No.: 1

Primer 1: 5′-CCN AAY YTN CAR AAY ATH-3′

SEQ ID No.: 2

Primer 2: 5′-YTC RTC RTG NAC YTG-3′

The PCR amplification was performed in 100 μl buffer containing 750 ng of genomic DNA from Carboxydothermus hydrogenoformans, 10 mM Tris-HCl, pH 8.8. 2.5 mM MgCl₂, 50 mM KCl, 200 μM dNTPs, 100 pmoles of each primer and 2.5 units of Taq polymerase (Boehringer Mannheim GmbH, FRG). The target sequence was amplified by first denaturing at 95° C. for 2 min. followed by 30 cycles of 95° C. for 0.5 min. 47° C. for 1 min. and 72° C. for 2 minutes. Thermal cycling was performed in a Perkin Elmer GenAmp 9600 thermal cycler. Agarose gel electrophoresis showed, that a fragment of approximately 600 base pairs was amplified specifically. This fragment was ligated into the pCR™ II vector (Invitrogen) and the sequence determined by cycle-sequencing. The amino acid sequence deduced from this nucleotide sequence was very similar to that of other known DNA polymerases, so that primer 3 and 4 could be designed for inverse PCR.

SEQ ID No.: 3

Primer 3: 5′-GGG CGA AGA CGC TAT ATT CCT GAG C-3′

SEQ ID No.: 4

Primer 4: 5′-GAA GCC TTA ATT CAA TCT GGG AAT AAT C-3′

Inverse PCR was performed essentially as described in Triglia T. et al. (1988) Nucleic Acids Res. 16, 8186. 5 μg genomic DNA from Carboxydothermus hydrogenoformans were cleaved by EcoRI according to supplier's specifications (Boehringer Mannheim GmbH) and treated with an equal volume of phenol/chloroform mixture. The aqueous phase was removed, the DNA precipitated with ethanol and collected by centrifugation.

For circularization the digested DNA was diluted to a concentration of 50 ng/μl in ligation buffer (Boehringer Mannheim GmbH, FRG). The ligation reaction was initiated by the addition of T4 DNA Ligase (Boehringer Mannheim GmbH, FRG) to a concentration of 0.2 units/μl and the reaction was allowed to proceed for 15 hrs at 15° C. The ligated DNA was then precipitated with ethanol and collected by centrifugation.

The PCR was performed in 50 μl buffer containing 50 mM Tris-Cl, pH 9.2, 16 mM (NH₄)₂SO₄, 2.25 mM MgCl₂, 2% (v/v) DMSO, 0.1% (v/v) Tween™ 20, 700 ng of circularized DNA obtained as described above, 50 pmoles of each primer. 500 μM dNTP and 0.75 μl enzyme mix (Expand Long Template PCR System, Boehringer Mannheim GmbH).

The cycle conditions were as follows:

1×denaturation of template for 2 min. at 92° C. $10 \times \left\lbrack {\begin{matrix} {{denaturation}\quad {at}\quad 92{^\circ}\quad {C.\quad {for}}\quad 10\quad {\sec.}} \\ {{annealing}\quad {at}\quad 64{^\circ}\quad {C.\quad {for}}\quad 30\quad {\sec.}} \\ {{elongation}\quad {at}\quad 68{^\circ}\quad {C.\quad {for}}\quad 2\quad {\min.}} \end{matrix}20 \times \left\lbrack \begin{matrix} {{denaturation}\quad {at}\quad 92{^\circ}\quad {C.\quad {for}}\quad 10\quad {\sec.}} \\ {{annealing}\quad {at}\quad 64{^\circ}\quad {C.\quad {for}}\quad 30\quad {\sec.}} \\ {{elongation}\quad {at}\quad 68{^\circ}\quad {C.\quad {for}}\quad 2\quad {\min. +}} \\ {{cycle}\quad {elongation}\quad {of}\quad 20\quad {\sec.\quad {for}}\quad {each}\quad {cycle}} \end{matrix} \right.} \right.$

Agarose gel electrophoresis revealed a specifically amplified DNA fragment 7.000 base pairs long. The DNA fragment was ligated into the pCR™ II vector (Invitrogen) and sequenced. Deduced from this sequence primer 5 and 6 coding for the 5′- and 3′-ends, respectively, of the polymerase region could be designed. Primer 5 contained a NcoI site and primer 6 contained a BamHI site. The PCR was performed under the same conditions as described above (inverse PCR) using 750 ng genomic DNA from Carboxydothermus hydrogenoformans as template.

SEQ ID No.: 5

Primer 5: 5′-CGA ATT CAA TCC ATG GGA AAA GTA GTC CTG GTG GAT-3′

SEQ ID No.: 6

Primer 6: 5′-CGA ATT CAA GGA TCC TTA CTT CGC TTC ATA CCA GTT-3′

Cloning and Expression

The PCR product was purified by electrophoresis of 20 μl of the PCR mixture on a 0.8% agarose gel. The 2.496 kb band of the polymerase coding region was purified from the agarose by phenol extraction. The DNA was then treated with chloroform and precipitated with ethanol. The pellet was resuspended and digested with NcoI and BamHI according to supplier's specifications (Boehringer Mannheim GmbH) to give cohesive ends for directional cloning. The DNA was ligated into the expression vector pDS56 (Stüber D., Matile H. and Garotta G. (1990) Immunological Methods, Letkovcs, I and Penis, B., eds.) that had also been digested with NcoI and BamHI. The ligated products were introduced into E.coli strain BL21(DE3) pUBS520 (Brinkmann U. et at. (1989) Gene 85, 109-114) by transformation. Transformants were grown on L-agar containing 100 μg/ml ampicillin and 50 μg/ml kanamycin to allow selection of recombinants. Colonies were picked and grown in L-broth containing 100 μg/ml ampicillin and 50 μg/ml kanamycin, and plasmid DNA was prepared by alkaline lysis. The plasmids were screened for insertions by digestion with BamHI. Those recombinants containing inserts were grown in L-broth containing ampicillin and kanamycin and tested for the expression of thermophilic DNA polymerase by induction of exponentially growing culture with 1 mM IPTG and assaying the heat-treated extracts for DNA polymerase activity as described above (determination of DNA polymerase activity). A recombinant expressing the DNA polymerase from Carboxydothermus hydrogenoformans was obtained. The strain was designated E.coli AR96 (DSM No. 11179) and the plasmid pAR4.

9 1 18 DNA Artificial Sequence amplification primer 1 ccnaayytnc araayath 18 2 15 DNA Artificial Sequence amplification primer 2 ytcrtcrtgn acytg 15 3 25 DNA Artificial Sequence amplification primer 3 gggcgaagac gctatattcc tgagc 25 4 28 DNA Artificial Sequence amplification primer 4 gaagccttaa ttcaatctgg gaataatc 28 5 36 DNA Artificial Sequence amplification primer 5 cgaattcaat ccatgggaaa agtagtcctg gtggat 36 6 36 DNA Artificial Sequence amplification primer 6 cgaattcaag gatccttact tcgcttcata ccagtt 36 7 2496 DNA Carboxydothermus hydrogenoformans CDS (1)..(2496) 7 atg gga aaa gta gtc ctg gtg gat gga aat agt tta tta cat aga gcg 48 Met Gly Lys Val Val Leu Val Asp Gly Asn Ser Leu Leu His Arg Ala 1 5 10 15 ttt ttt gcc ctt ccg ccc tta aaa act act aaa gga gag cct acc ggg 96 Phe Phe Ala Leu Pro Pro Leu Lys Thr Thr Lys Gly Glu Pro Thr Gly 20 25 30 gcg gtt tac ggg ttt tta acg atg ctt ttt cgg gta ata aaa gat gaa 144 Ala Val Tyr Gly Phe Leu Thr Met Leu Phe Arg Val Ile Lys Asp Glu 35 40 45 aaa ccc gaa tat tta gcg gta gct ttt gat att agc cgg aaa act ttt 192 Lys Pro Glu Tyr Leu Ala Val Ala Phe Asp Ile Ser Arg Lys Thr Phe 50 55 60 cgt acc gag cag ttt act gca tac aaa ggg cac cgc aaa gaa gcc ccg 240 Arg Thr Glu Gln Phe Thr Ala Tyr Lys Gly His Arg Lys Glu Ala Pro 65 70 75 80 gat gag ctt gta ccc cag ttt gcc ctg gtg cgg gaa gta tta aag gtt 288 Asp Glu Leu Val Pro Gln Phe Ala Leu Val Arg Glu Val Leu Lys Val 85 90 95 tta aat gtt ccc tat att gaa ctt gac ggt tat gag gcc gat gat att 336 Leu Asn Val Pro Tyr Ile Glu Leu Asp Gly Tyr Glu Ala Asp Asp Ile 100 105 110 atc ggc cac cta tca agg gct ttt gcg gga caa gga cat gaa gtg gtg 384 Ile Gly His Leu Ser Arg Ala Phe Ala Gly Gln Gly His Glu Val Val 115 120 125 att tat acc gct gac cgg gac atg ctg caa ttg gta gat gaa aaa acg 432 Ile Tyr Thr Ala Asp Arg Asp Met Leu Gln Leu Val Asp Glu Lys Thr 130 135 140 gtg gta tac ctt acc aaa aaa ggc att acc gaa ctg gtt aaa atg gat 480 Val Val Tyr Leu Thr Lys Lys Gly Ile Thr Glu Leu Val Lys Met Asp 145 150 155 160 tta gct gcg att tta gaa aac tac ggc tta aag cct aaa cag ctt gtg 528 Leu Ala Ala Ile Leu Glu Asn Tyr Gly Leu Lys Pro Lys Gln Leu Val 165 170 175 gat gtt aaa gga tta atg gga gat ccc tcg gac aac ata ccc ggg gtt 576 Asp Val Lys Gly Leu Met Gly Asp Pro Ser Asp Asn Ile Pro Gly Val 180 185 190 ccc ggg att ggg gag aaa act gct tta gat tta att aaa act tat ggc 624 Pro Gly Ile Gly Glu Lys Thr Ala Leu Asp Leu Ile Lys Thr Tyr Gly 195 200 205 tca gtg gaa gaa gtt ttg gcc cgt aaa gat gag tta aaa cct aaa tta 672 Ser Val Glu Glu Val Leu Ala Arg Lys Asp Glu Leu Lys Pro Lys Leu 210 215 220 aga gaa aag ctt gcc gaa cac gaa aat tta gca aaa ata tcg aaa caa 720 Arg Glu Lys Leu Ala Glu His Glu Asn Leu Ala Lys Ile Ser Lys Gln 225 230 235 240 tta gct aca atc ctg cgg gaa ata ccg tta gaa atc tcc ctg gaa gat 768 Leu Ala Thr Ile Leu Arg Glu Ile Pro Leu Glu Ile Ser Leu Glu Asp 245 250 255 tta aaa gtt aaa gaa cct aat tat gaa gaa gtt gct aaa tta ttt ctt 816 Leu Lys Val Lys Glu Pro Asn Tyr Glu Glu Val Ala Lys Leu Phe Leu 260 265 270 cac ctt gag ttt aaa agc ttt tta aaa gaa ata gaa cca aaa ata aag 864 His Leu Glu Phe Lys Ser Phe Leu Lys Glu Ile Glu Pro Lys Ile Lys 275 280 285 aaa gaa tac cag gaa ggt aaa gat ttg gtg caa gtt gaa act gta gaa 912 Lys Glu Tyr Gln Glu Gly Lys Asp Leu Val Gln Val Glu Thr Val Glu 290 295 300 acg gaa gga cag att gca gta gtt ttt agt gat gga ttt tat gtt gat 960 Thr Glu Gly Gln Ile Ala Val Val Phe Ser Asp Gly Phe Tyr Val Asp 305 310 315 320 gac ggg gaa aaa aca aag ttt tac tct tta gac cgg ctg aat gaa ata 1008 Asp Gly Glu Lys Thr Lys Phe Tyr Ser Leu Asp Arg Leu Asn Glu Ile 325 330 335 gag gaa ata ttt agg aat aaa aaa att att acc gac gat gcc aaa gga 1056 Glu Glu Ile Phe Arg Asn Lys Lys Ile Ile Thr Asp Asp Ala Lys Gly 340 345 350 att tat cat gtc tgt tta gaa aaa ggt ctg act ttt ccc gaa gtt tgt 1104 Ile Tyr His Val Cys Leu Glu Lys Gly Leu Thr Phe Pro Glu Val Cys 355 360 365 ttt gat gcg cgg att gca gct tat gtt tta aac ccg gcc gac caa aat 1152 Phe Asp Ala Arg Ile Ala Ala Tyr Val Leu Asn Pro Ala Asp Gln Asn 370 375 380 ccc ggc ctc aag ggg ctt tat cta aag tat gac tta ccg gtg tat gaa 1200 Pro Gly Leu Lys Gly Leu Tyr Leu Lys Tyr Asp Leu Pro Val Tyr Glu 385 390 395 400 gat gta tct tta aac att aga ggg ttg ttt tat tta aaa aaa gaa atg 1248 Asp Val Ser Leu Asn Ile Arg Gly Leu Phe Tyr Leu Lys Lys Glu Met 405 410 415 atg aga aaa atc ttt gag cag gag caa gaa agg tta ttt tat gaa ata 1296 Met Arg Lys Ile Phe Glu Gln Glu Gln Glu Arg Leu Phe Tyr Glu Ile 420 425 430 gaa ctt cct tta act cca gtt ctt gct caa atg gag cat acc ggc att 1344 Glu Leu Pro Leu Thr Pro Val Leu Ala Gln Met Glu His Thr Gly Ile 435 440 445 cag gtt gac cgg gaa gct tta aaa gag atg tcg tta gag ctg gga gag 1392 Gln Val Asp Arg Glu Ala Leu Lys Glu Met Ser Leu Glu Leu Gly Glu 450 455 460 caa att gaa gag tta atc cgg gaa att tat gtg ctg gcg ggg gaa gag 1440 Gln Ile Glu Glu Leu Ile Arg Glu Ile Tyr Val Leu Ala Gly Glu Glu 465 470 475 480 ttt aac tta aac tcg ccc agg cag ctg gga gtt att ctt ttt gaa aaa 1488 Phe Asn Leu Asn Ser Pro Arg Gln Leu Gly Val Ile Leu Phe Glu Lys 485 490 495 ctt ggg ctg ccg gta att aaa aag acc aaa acg ggc tac tct acc gat 1536 Leu Gly Leu Pro Val Ile Lys Lys Thr Lys Thr Gly Tyr Ser Thr Asp 500 505 510 gcg gag gtt ttg gaa gag ctc ttg cct ttc cac gaa att ggc atc ggc 1584 Ala Glu Val Leu Glu Glu Leu Leu Pro Phe His Glu Ile Gly Ile Gly 515 520 525 aaa ata ttg aat tac cgg cag ctt atg aag tta aaa tcc act tat act 1632 Lys Ile Leu Asn Tyr Arg Gln Leu Met Lys Leu Lys Ser Thr Tyr Thr 530 535 540 gac tta atg cct tta ata aat gag cgt acc ggt aaa ctt cac act act 1680 Asp Leu Met Pro Leu Ile Asn Glu Arg Thr Gly Lys Leu His Thr Thr 545 550 555 560 ttt aac cag acc ggt act tta acc gga cgc ctg gcg tct tcg gag ccc 1728 Phe Asn Gln Thr Gly Thr Leu Thr Gly Arg Leu Ala Ser Ser Glu Pro 565 570 575 aat ctc caa aat att ccc atc cgg ttg gaa ctc ggt cgg aaa tta cgc 1776 Asn Leu Gln Asn Ile Pro Ile Arg Leu Glu Leu Gly Arg Lys Leu Arg 580 585 590 aag atg ttt ata cct tca ccg ggg tat gat tat att gtt tcg gcg gat 1824 Lys Met Phe Ile Pro Ser Pro Gly Tyr Asp Tyr Ile Val Ser Ala Asp 595 600 605 tat tcc cag att gaa tta agg ctt ctt gcc cat ttt tcc gaa gag ccc 1872 Tyr Ser Gln Ile Glu Leu Arg Leu Leu Ala His Phe Ser Glu Glu Pro 610 615 620 aag ctt att gaa gct tac caa aaa ggg gag gat att cac cgg aaa acg 1920 Lys Leu Ile Glu Ala Tyr Gln Lys Gly Glu Asp Ile His Arg Lys Thr 625 630 635 640 gcc tcc gag gtg ttc ggt gta tct ttg gaa gaa gtt act ccc gag atg 1968 Ala Ser Glu Val Phe Gly Val Ser Leu Glu Glu Val Thr Pro Glu Met 645 650 655 cgc gct cat gcc aag tcg gtg aac ttc ggc att gtt tat ggc att agt 2016 Arg Ala His Ala Lys Ser Val Asn Phe Gly Ile Val Tyr Gly Ile Ser 660 665 670 gat ttt ggt tta ggc aga gac tta aag att ccc cgg gag gtt gcc ggt 2064 Asp Phe Gly Leu Gly Arg Asp Leu Lys Ile Pro Arg Glu Val Ala Gly 675 680 685 aag tac att aaa aat tat ttt gcc aac tat ccc aaa gtg cgg gag tat 2112 Lys Tyr Ile Lys Asn Tyr Phe Ala Asn Tyr Pro Lys Val Arg Glu Tyr 690 695 700 ctc gat gaa ctt gtc cgt acg gca aga gaa aag gga tat gtg acc act 2160 Leu Asp Glu Leu Val Arg Thr Ala Arg Glu Lys Gly Tyr Val Thr Thr 705 710 715 720 tta ttt ggg cga aga cgc tat att cct gag cta tct tca aaa aac cgc 2208 Leu Phe Gly Arg Arg Arg Tyr Ile Pro Glu Leu Ser Ser Lys Asn Arg 725 730 735 acg gtt cag ggt ttt ggc gaa agg acg gcc atg aat act ccc ctt cag 2256 Thr Val Gln Gly Phe Gly Glu Arg Thr Ala Met Asn Thr Pro Leu Gln 740 745 750 ggc tcg gct gcc gat att att aag ctt gca atg att aat gta gaa aaa 2304 Gly Ser Ala Ala Asp Ile Ile Lys Leu Ala Met Ile Asn Val Glu Lys 755 760 765 gaa ctt aaa gcc cgt aag ctt aag tcc cgg ctc ctt ctt tcg gtg cac 2352 Glu Leu Lys Ala Arg Lys Leu Lys Ser Arg Leu Leu Leu Ser Val His 770 775 780 gat gag tta gtt tta gaa gtg ccg gcg gaa gag ctg gaa gag gta aaa 2400 Asp Glu Leu Val Leu Glu Val Pro Ala Glu Glu Leu Glu Glu Val Lys 785 790 795 800 gcg ctg gta aaa ggg gtt atg gag tcg gtg gtt gaa ctg aaa gtg cct 2448 Ala Leu Val Lys Gly Val Met Glu Ser Val Val Glu Leu Lys Val Pro 805 810 815 tta atc gct gaa gtt ggt gca ggc aaa aac tgg tat gaa gcg aag taa 2496 Leu Ile Ala Glu Val Gly Ala Gly Lys Asn Trp Tyr Glu Ala Lys 820 825 830 8 831 PRT Carboxydothermus hydrogenoformans 8 Met Gly Lys Val Val Leu Val Asp Gly Asn Ser Leu Leu His Arg Ala 1 5 10 15 Phe Phe Ala Leu Pro Pro Leu Lys Thr Thr Lys Gly Glu Pro Thr Gly 20 25 30 Ala Val Tyr Gly Phe Leu Thr Met Leu Phe Arg Val Ile Lys Asp Glu 35 40 45 Lys Pro Glu Tyr Leu Ala Val Ala Phe Asp Ile Ser Arg Lys Thr Phe 50 55 60 Arg Thr Glu Gln Phe Thr Ala Tyr Lys Gly His Arg Lys Glu Ala Pro 65 70 75 80 Asp Glu Leu Val Pro Gln Phe Ala Leu Val Arg Glu Val Leu Lys Val 85 90 95 Leu Asn Val Pro Tyr Ile Glu Leu Asp Gly Tyr Glu Ala Asp Asp Ile 100 105 110 Ile Gly His Leu Ser Arg Ala Phe Ala Gly Gln Gly His Glu Val Val 115 120 125 Ile Tyr Thr Ala Asp Arg Asp Met Leu Gln Leu Val Asp Glu Lys Thr 130 135 140 Val Val Tyr Leu Thr Lys Lys Gly Ile Thr Glu Leu Val Lys Met Asp 145 150 155 160 Leu Ala Ala Ile Leu Glu Asn Tyr Gly Leu Lys Pro Lys Gln Leu Val 165 170 175 Asp Val Lys Gly Leu Met Gly Asp Pro Ser Asp Asn Ile Pro Gly Val 180 185 190 Pro Gly Ile Gly Glu Lys Thr Ala Leu Asp Leu Ile Lys Thr Tyr Gly 195 200 205 Ser Val Glu Glu Val Leu Ala Arg Lys Asp Glu Leu Lys Pro Lys Leu 210 215 220 Arg Glu Lys Leu Ala Glu His Glu Asn Leu Ala Lys Ile Ser Lys Gln 225 230 235 240 Leu Ala Thr Ile Leu Arg Glu Ile Pro Leu Glu Ile Ser Leu Glu Asp 245 250 255 Leu Lys Val Lys Glu Pro Asn Tyr Glu Glu Val Ala Lys Leu Phe Leu 260 265 270 His Leu Glu Phe Lys Ser Phe Leu Lys Glu Ile Glu Pro Lys Ile Lys 275 280 285 Lys Glu Tyr Gln Glu Gly Lys Asp Leu Val Gln Val Glu Thr Val Glu 290 295 300 Thr Glu Gly Gln Ile Ala Val Val Phe Ser Asp Gly Phe Tyr Val Asp 305 310 315 320 Asp Gly Glu Lys Thr Lys Phe Tyr Ser Leu Asp Arg Leu Asn Glu Ile 325 330 335 Glu Glu Ile Phe Arg Asn Lys Lys Ile Ile Thr Asp Asp Ala Lys Gly 340 345 350 Ile Tyr His Val Cys Leu Glu Lys Gly Leu Thr Phe Pro Glu Val Cys 355 360 365 Phe Asp Ala Arg Ile Ala Ala Tyr Val Leu Asn Pro Ala Asp Gln Asn 370 375 380 Pro Gly Leu Lys Gly Leu Tyr Leu Lys Tyr Asp Leu Pro Val Tyr Glu 385 390 395 400 Asp Val Ser Leu Asn Ile Arg Gly Leu Phe Tyr Leu Lys Lys Glu Met 405 410 415 Met Arg Lys Ile Phe Glu Gln Glu Gln Glu Arg Leu Phe Tyr Glu Ile 420 425 430 Glu Leu Pro Leu Thr Pro Val Leu Ala Gln Met Glu His Thr Gly Ile 435 440 445 Gln Val Asp Arg Glu Ala Leu Lys Glu Met Ser Leu Glu Leu Gly Glu 450 455 460 Gln Ile Glu Glu Leu Ile Arg Glu Ile Tyr Val Leu Ala Gly Glu Glu 465 470 475 480 Phe Asn Leu Asn Ser Pro Arg Gln Leu Gly Val Ile Leu Phe Glu Lys 485 490 495 Leu Gly Leu Pro Val Ile Lys Lys Thr Lys Thr Gly Tyr Ser Thr Asp 500 505 510 Ala Glu Val Leu Glu Glu Leu Leu Pro Phe His Glu Ile Gly Ile Gly 515 520 525 Lys Ile Leu Asn Tyr Arg Gln Leu Met Lys Leu Lys Ser Thr Tyr Thr 530 535 540 Asp Leu Met Pro Leu Ile Asn Glu Arg Thr Gly Lys Leu His Thr Thr 545 550 555 560 Phe Asn Gln Thr Gly Thr Leu Thr Gly Arg Leu Ala Ser Ser Glu Pro 565 570 575 Asn Leu Gln Asn Ile Pro Ile Arg Leu Glu Leu Gly Arg Lys Leu Arg 580 585 590 Lys Met Phe Ile Pro Ser Pro Gly Tyr Asp Tyr Ile Val Ser Ala Asp 595 600 605 Tyr Ser Gln Ile Glu Leu Arg Leu Leu Ala His Phe Ser Glu Glu Pro 610 615 620 Lys Leu Ile Glu Ala Tyr Gln Lys Gly Glu Asp Ile His Arg Lys Thr 625 630 635 640 Ala Ser Glu Val Phe Gly Val Ser Leu Glu Glu Val Thr Pro Glu Met 645 650 655 Arg Ala His Ala Lys Ser Val Asn Phe Gly Ile Val Tyr Gly Ile Ser 660 665 670 Asp Phe Gly Leu Gly Arg Asp Leu Lys Ile Pro Arg Glu Val Ala Gly 675 680 685 Lys Tyr Ile Lys Asn Tyr Phe Ala Asn Tyr Pro Lys Val Arg Glu Tyr 690 695 700 Leu Asp Glu Leu Val Arg Thr Ala Arg Glu Lys Gly Tyr Val Thr Thr 705 710 715 720 Leu Phe Gly Arg Arg Arg Tyr Ile Pro Glu Leu Ser Ser Lys Asn Arg 725 730 735 Thr Val Gln Gly Phe Gly Glu Arg Thr Ala Met Asn Thr Pro Leu Gln 740 745 750 Gly Ser Ala Ala Asp Ile Ile Lys Leu Ala Met Ile Asn Val Glu Lys 755 760 765 Glu Leu Lys Ala Arg Lys Leu Lys Ser Arg Leu Leu Leu Ser Val His 770 775 780 Asp Glu Leu Val Leu Glu Val Pro Ala Glu Glu Leu Glu Glu Val Lys 785 790 795 800 Ala Leu Val Lys Gly Val Met Glu Ser Val Val Glu Leu Lys Val Pro 805 810 815 Leu Ile Ala Glu Val Gly Ala Gly Lys Asn Trp Tyr Glu Ala Lys 820 825 830 9 22 DNA Artificial Sequence amplification primer 9 gcatggatcc cactgcccag gg 22 

We claim:
 1. An isolated DNA polymerase comprising SEQ ID NO:8.
 2. An isolated DNA sequence encoding the DNA polymerase of claim
 1. 3. An isolated DNA sequence comprising SEQ ID NO:7.
 4. A vector comprising a DNA sequence which encodes SEQ ID NO:8 comprising a DNA sequence which encodes SEQ ID NO:8.
 5. The vector of claim 4 that is pAR4.
 6. A host cell comprising the vector of claim 4 or
 5. 7. The host cell of claim 6 that is AR96.
 8. A vector comprising SEQ ID NO:
 7. 